A number of medicament delivery devices have been developed wherein a medicament container is placed inside the housing of the devices. The medicament container has to be supported in an appropriate manner in order to minimize the risk of breakage, which is a pronounced risk when the containers often are made of glass and wherein the force of a power pack, comprising a compression spring, often provide strong forces.
On the other hand, due to manufacturing aspects, as few components as possible are favoured, especially for disposable medicament delivery devices in order to keep the costs as low as possible.
With these aspects in mind some developments have been made. For instance the document US 2007/0021718 discloses the use of a compression spring for elastically supporting a medicament container in place in a housing of a medicament delivery device. The spring may be positioned between a distal end surface of the medicament container and an insert which is secured axially in the housing. The spring is preferably made of a plastic material.
Further, often when compression springs are used, some sort of support is required for preventing buckling of the spring. One common solution is then to have a guide rod extending inside the compression spring, such as is disclosed for example in WO 2013/032389. Another solution is to have a hollow plunger rod that is extra long and to place the compression spring inside the plunger rod.
A drawback with the use of a guide rod is that an extra component is needed, which component is not optimal from an assembly point of view of a power unit, because it has to be attached to a distal end wall of the medicament delivery device. On the other hand, the use of very long plunger rods is not optimal from a design point of view because the medicament delivery devices become long and not very attractive for an end user.